U.S. patent application number 14/168357 was filed with the patent office on 2014-08-14 for fixing device and image forming apparatus incorporating same.
The applicant listed for this patent is Kazuhito KISHI. Invention is credited to Kazuhito KISHI.
Application Number | 20140226999 14/168357 |
Document ID | / |
Family ID | 51297499 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140226999 |
Kind Code |
A1 |
KISHI; Kazuhito |
August 14, 2014 |
FIXING DEVICE AND IMAGE FORMING APPARATUS INCORPORATING SAME
Abstract
A fixing device includes a fixing member, a pressing member, a
heating unit, multiple sub-heaters disposed in the heating unit, a
temperature sensor to detect a temperature of the heating unit, and
a heating control unit. The heating control unit controls the
heating unit by controlling the multiple sub-heaters individually
to heat the respective heating areas, such that a temperature at a
portion of the fixing member corresponding to a blank area of the
recording medium is lower than a temperature of a portion of the
fixing member corresponding to an imaged area of the recording
medium. The heating control unit further changes a size of a
preliminary heating area to preliminarily heat the respective
heating areas before the imaged area enters the fixing nip
according to the temperature detected by the temperature
sensor.
Inventors: |
KISHI; Kazuhito; (Kanagawa,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KISHI; Kazuhito |
Kanagawa |
|
JP |
|
|
Family ID: |
51297499 |
Appl. No.: |
14/168357 |
Filed: |
January 30, 2014 |
Current U.S.
Class: |
399/69 ;
399/334 |
Current CPC
Class: |
G03G 15/2039 20130101;
G03G 15/2042 20130101 |
Class at
Publication: |
399/69 ;
399/334 |
International
Class: |
G03G 15/20 20060101
G03G015/20 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2013 |
JP |
2013-026533 |
Dec 20, 2013 |
JP |
2013-263681 |
Claims
1. A fixing device to fix an unfixed image on a recording material
in a fixing nip, the fixing device comprising: a rotatable fixing
member to contact the unfixed image; a pressing member to contact
the fixing member and form the fixing nip between the pressing
member and the fixing member; a heating unit to heat the fixing
member with electric power from a power source; multiple
sub-heaters disposed in the heating unit to heat respective heating
areas, arrayed in a direction perpendicular to a direction in which
a recording material is conveyed; a temperature sensor to detect a
temperature of the heating unit; and a heating control unit to
control the heating unit by controlling the multiple sub-heaters
individually to heat the respective heating areas, such that a
temperature at a portion of the fixing member corresponding to a
blank area of the recording medium is lower than a temperature of a
portion of the fixing member corresponding to an imaged area of the
recording medium, the heating control unit further changing a size
of a preliminary heating area to preliminarily heat the respective
heating areas before the imaged area enters the fixing nip
according to the temperature detected by the temperature
sensor.
2. The fixing device according to claim 1, wherein the heating unit
is a heating element configured to contact the fixing member to
increase a temperature of the fixing member, and the heating
control unit sets the preliminary heating area to be smaller than a
reference preliminary heating area when the temperature sensor
detects a temperature of the heating unit higher than a
predetermined temperature.
3. The fixing device according to claim 2, wherein the heating
control unit sets the preliminary heating area to be equal to or
larger than a reference preliminary heating area when the
temperature sensor detects a temperature of the heating unit not
higher than the predetermined temperature.
4. The fixing device according to claim 1, wherein the heating
control unit sets the preliminary heating area to be smaller than a
reference preliminary heating area when a voltage of the power
source exceeds a predetermined voltage.
5. The fixing device according to claim 1, wherein the heating
control unit has multiple threshold temperatures for changing the
size of the preliminary heating area according to the temperature
detected by the temperature sensor.
6. An image forming apparatus comprising the fixing device
according to claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is based on and claims priority
pursuant to 35 U.S.C. .sctn.119 to Japanese Patent Application Nos.
2013-026533, filed on Feb. 14, 2013, and 2013-263681, filed on Dec.
20, 2013, in the Japan Patent Office, the entire disclosures of
which are hereby incorporated by reference herein.
BACKGROUND
[0002] 1. Technical Field
[0003] Embodiments of this disclosure generally relate to a fixing
device employing a heating method and to an electrophotographic
image forming apparatus, such as a copier, a printer, or a
facsimile machine, incorporating the fixing device.
[0004] 2. Related Art
[0005] Image forming apparatuses, such as copiers, facsimile
machines, or printers usually form a toner image on an image
carrier according to image data. The toner image is transferred
from the image carrier onto a recording medium such as a sheet of
paper or an overhead projector (OHP) sheet. The recording medium
carrying the toner image is then conveyed to a fixing device, in
which the toner image is fixed onto the recording medium under heat
and pressure.
[0006] Fixing devices employing a heat-roller method usually
include a fixing roller and a pressing roller. The fixing roller is
heated by a heat source such as a halogen heater or an induction
heating coil. The fixing roller and the pressing roller press
against each other to form an area of contact herein called a nip,
to which a recording medium carrying a toner image is conveyed.
Toner included in the toner image is fused under heat and pressure
in the nip. Thus, the toner image is fixed onto the recording
medium. Such fixing devices are widely used for safety and
adaptability to high-speed machines.
[0007] However, it takes a few minutes for the fixing roller,
typically having a metal core and a large heat capacity, to reach a
predetermined fixing temperature. Hence, the fixing roller is
maintained at a predetermined temperature during standby time,
resulting in relatively large energy consumption.
[0008] By contrast, fixing devices employing a belt or film method
are frequently used for energy efficiency. Several energy-efficient
fixing techniques employed with such fixing devices have been
proposed, such as those externally heating a thermal insulating
roller or selectively heating an imaged area according to the image
data.
[0009] For example, JP-H06-095540-A discloses a fixing device
employing the film method, in which a pressing roller and a planar
heater that contact a thin, cylindrical film having thermal
resistance sandwiches the film and a recording material so that the
film and the recording material adhere to each other, thereby
heating the recording material. Because the film has a thickness of
only about 100 .mu.m, in actuality the fixing device can be warmed
up simply by increasing the temperature of the low heat-capacity
planar heater. Accordingly, the warm-up time can be shortened and
the preheating power can be reduced.
[0010] In addition, JP-H06-095540-A discloses a technique whereby
the temperature of the heater and the heating areas are changed
based on an image formed on the recording material to reduce energy
supply to a blank area (i.e., a portion of an image formation area
without an image), thereby enhancing energy efficiency.
[0011] JP-2005-181946-A discloses a technique whereby the
temperature of a thermal heater is measured for each heating
element to supply appropriate heat, thereby heating only a portion
where toner exists on a surface of a sheet, taking into account the
surrounding temperature.
[0012] JP-2001-343860 employs a fixing method to externally heat a
roller. The external heating allows toner to be fused by heat
accumulated on and around a fixing roller. Accordingly, such an
external heating method realizes a shorter warm-up time and a
higher energy efficiency than an internal heating method to heat an
entire fixing roller. As in JP-H06-095540-A and JP-2005-181946-A,
JP-2001-343860 discloses that imaged areas are selectively heated
and that a second target temperature is provided which is lower
than a target fixing temperature.
[0013] Typical fixing devices are supplied with a maximum energy
sufficient to fix an image formed on an entire surface of a
recording material.
[0014] However, when an imaged area is selectively heated, electric
power is supplied before that imaged area enters the fixing nip. In
other words, a preliminary heating area is provided, taking into
account a predetermined time taken to warm up a heating member
including a heat generator. The preliminary heating area is
provided in a blank area that does not bear an unfixed toner image.
Hence, the preliminary heating area is preferably as small as
possible.
SUMMARY
[0015] This specification describes below an improved fixing
device. In one embodiment of this disclosure, the fixing device
fixes an unfixed image on a recording material in a fixing nip and
including a rotatable fixing member to contact the unfixed image, a
pressing member to contact the fixing member and form the fixing
nip between the pressing member and the fixing member, a heating
unit to heat the fixing member with electric power from a power
source, multiple sub-heaters disposed in the heating unit to heat
respective heating areas, arrayed in a direction perpendicular to a
direction in which a recording material is conveyed, and a
temperature sensor to detect a temperature of the heating unit. The
fixing device further includes a heating control unit to control
the heating unit by controlling the multiple sub-heaters
individually to heat the respective heating areas, such that a
temperature at a portion of the fixing member corresponding to a
blank area of the recording medium is lower than a temperature of a
portion of the fixing member corresponding to an imaged area of the
recording medium. The heating control unit further changes a size
of a preliminary heating area to preliminarily heat the respective
heating areas before the imaged area enters the fixing nip
according to the temperature detected by the temperature
sensor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] A more complete appreciation of the disclosure and many of
the attendant advantages thereof will be more readily obtained as
the same becomes better understood by reference to the following
detailed description of embodiments when considered in connection
with the accompanying drawings, wherein:
[0017] FIG. 1 is a schematic sectional view of an image forming
apparatus according to embodiments;
[0018] FIG. 2 is a schematic sectional view of a fixing device
according to a first embodiment;
[0019] FIG. 3 is a partial perspective view of the fixing device of
FIG. 2;
[0020] FIG. 4A is a plan view of a sheet, illustrating imaged areas
and a blank area of the sheet;
[0021] FIG. 4B is a plan view of a sheet, illustrating an imaged
area and a blank area of the sheet;
[0022] FIG. 5A is a plan view of a sheet, illustrating an imaged
area and a blank area of the sheet;
[0023] FIG. 5B is a plan view of a sheet, illustrating imaged areas
and a blank area of the sheet;
[0024] FIG. 6 is a schematic sectional view of a fixing device
according to a second embodiment;
[0025] FIG. 7 is a schematic view of a heater including ten
sub-heaters;
[0026] FIG. 8 is a schematic sectional view of a fixing device
according to a third embodiment;
[0027] FIG. 9 is a schematic sectional view of a fixing device
according to a fourth embodiment;
[0028] FIG. 10 is a schematic view of a fixing device employing an
external heating method;
[0029] FIG. 11 is a plan view of a sheet, illustrating imaged
areas, blank areas, and preliminary heating areas of the sheet;
[0030] FIG. 12 is a graph of a relationship between target
temperatures and roller portions;
[0031] FIG. 13 is a graph of a relationship between target
temperatures and roller portions, particularly illustrating the
relationship between the target temperatures and the roller
portions corresponding to preliminary heating areas; and
[0032] FIG. 14 is a flowchart of a process for setting a
preliminary heating area according to detection results of the
sub-heaters.
[0033] The accompanying drawings are intended to depict embodiments
of this disclosure and should not be interpreted to limit the scope
thereof. The accompanying drawings are not to be considered as
drawn to scale unless explicitly noted.
DETAILED DESCRIPTION
[0034] In describing embodiments illustrated in the drawings,
specific terminology is employed for the sake of clarity. However,
the disclosure of this patent specification is not intended to be
limited to the specific terminology so selected and it is to be
understood that each specific element includes all technical
equivalents that have the same function, operate in a similar
manner, and achieve similar results.
[0035] Although the embodiments are described with technical
limitations with reference to the attached drawings, such
description is not intended to limit the scope of the invention and
all of the components or elements described in the embodiments of
this disclosure are not necessarily indispensable to the present
invention.
[0036] In a later-described comparative example, embodiment, and
exemplary variation, for the sake of simplicity like reference
numerals will be given to identical or corresponding constituent
elements such as parts and materials having the same functions, and
redundant descriptions thereof will be omitted unless otherwise
required.
[0037] Referring now to the drawings, wherein like reference
numerals designate identical or corresponding parts throughout the
several views, embodiments of this disclosure are described
below.
[0038] Initially with reference to FIG. 1, a description is given
of an image forming apparatus 2 according to embodiments of this
disclosure.
[0039] FIG. 1 is a schematic sectional view of the image forming
apparatus 2 according to embodiments of this disclosure.
[0040] As illustrated in FIG. 1, the image forming apparatus 2,
herein serving as a printer, includes, e.g., a sheet-feeding unit
4, a pair of registration rollers 6, a photoconductive drum 8
serving as an image carrier, a transfer unit 10, and a fixing
device 12.
[0041] The sheet-feeding unit 4 includes, e.g., a sheet tray 14 and
a sheet-feeding roller 16. The sheet tray 14 accommodates a stack
of sheets P serving as recording media. The sheet-feeding roller 16
sequentially separates and feeds an uppermost sheet P from the
stack of sheets P accommodated in the sheet tray 14. The pair of
registration rollers 6 temporarily stops the uppermost sheet P fed
by the sheet-feeding roller 16 to correct the position of the sheet
P. The sheet P is then conveyed to a transfer nip N from the pair
of registration rollers 6 in synchronization with rotation of the
photoconductive drum 8, that is, in a manner such that a leading
end of a toner image formed on the photoconductive drum 8 meets a
predetermined portion at a leading end of the sheet P in a
direction in which the sheet P is conveyed.
[0042] The photoconductive drum 8 is surrounded by various pieces
of imaging equipment disposed in a direction indicated by arrow X.
Specific examples of such imaging equipment include, but are not
limited to, a charging roller 18 serving as a charging unit, a
mirror 20 included in an exposure unit, a development unit 22
including a development roller 22a, a transfer unit 10, and a
cleaning unit 24 including a cleaning blade 24a. A laser beam Lb is
directed onto an exposure part 26 on the photoconductive drum 8 via
the mirror 20, between the charging roller 18 and the development
unit 22, and an outer surface of the photoconductive drum 8 at the
exposure part 26 is scanned.
[0043] A description is now given of operation of the image forming
apparatus 2. The image forming apparatus 2 performs imaging
operation in the same manner as typical image forming apparatuses.
When the photoconductive drum 8 starts to rotate, the charging
roller 18 uniformly charges the outer surface of the
photoconductive drum 8. The light beam Lb is directed and scanned
to the exposure part 26 according to image data to form an
electrostatic latent image corresponding to a target image.
[0044] The rotation of the photoconductive drum 8 moves the
electrostatic latent image to the development unit 22. The
development unit 22 develops the electrostatic latent image by
supplying toner to the electrostatic latent image to form a visible
image, also known as a toner image. The toner image thus formed on
the photoconductive drum 8 is transferred onto the sheet P, which
enters the transfer nip N in a predetermined timing, with a
transfer bias applied by the transfer unit 10. The sheet P carrying
the toner image is conveyed toward the fixing device 12. The fixing
device 12 fixes the toner image onto the sheet P. The sheet P is
then outputted to an output tray, in which multiple sheets P are
stacked one atop another.
[0045] Residual toner remaining on the photoconductive drum 8 after
a transfer process conducted at the transfer nip N reaches the
cleaning unit 24 by the rotation of the photoconductive drum 8. The
residual toner on the photoconductive drum 8 is scraped off, and
thus removed by the cleaning blade 24a while passing through the
cleaning unit 24. A neutralizing unit then removes residual charge
on the photoconductive drum 8, thereby preparing for a next imaging
process.
[0046] Referring now to FIGS. 2 and 3, a description is now given
of a fixing device 12 according to a first embodiment, which
employs an external heating method.
[0047] FIG. 2 is a schematic sectional view of the fixing device 12
according to the first embodiment.
[0048] The fixing device 12 includes, e.g., a fixing roller 28, a
pressing roller 30, and a heater 56. The fixing roller 28 serves as
a fixing member to rotate while contacting an unfixed image. The
pressing roller 30 serves as a pressing member to form a fixing nip
SN between the pressing roller 30 and the fixing roller 28. The
heater 56 serves as a heating unit to heat the fixing roller 28
with electric power supplied from a commercial power source 40. The
heater 56 may be, e.g., a thermal heater or ceramic heater,
including a planar base and a heating element disposed on the
planar base. The heater 56 herein serves as an external heating
unit supplied with the electric power from the power source 40.
[0049] As illustrated in FIG. 3, the heater 56 includes multiple
sub-heaters, which, in the present embodiment, are seven
sub-heaters 56a through 56g, arrayed at a predetermined interval in
a width direction of a sheet P. The sub-heaters 56a through 56g are
configured to separately heat respective heating areas.
[0050] Referring back to FIG. 2, thermistors 34 and 36, the power
source 40, and an external heating control unit 42 are disposed
downstream from the fixing nip SN and upstream from the heater 56
in a direction indicated by an arrow Y, in which the fixing roller
28 rotates. The thermistor 34 serves as a temperature sensor to
detect a surface temperature of the fixing roller 28. The
thermistor 36 serves as a temperature sensor to detect a
temperature of the heater 56. The power source 40 supplies electric
power to the heater 56. The external heating control unit 42
controls the power source 40 according to detection data of the
thermistors 34 and 36.
[0051] The external heating control unit 42 is herein constituted
as a microprocessor including, e.g., a central processing unit
(CPU), a read-only memory (ROM), a random-access memory (RAM), and
an input/output (I/O) interface.
[0052] The fixing roller 28 is constructed of a metal core 28a, a
heat insulation layer 28b, a heat conductive layer 28c, and a
release layer 28d.
[0053] The metal core 28a is made of aluminum and has an outer
diameter of about 50 mm and a thickness of about 3 mm.
[0054] The heat insulation layer 28b coats an outer surface of the
metal core 28a. The heat insulation layer 28b is made of silicone
rubber and has a thickness of about 4 mm. The heat insulation layer
28b may be made of foam silicone rubber to prevent heat diffusion
and enhance heat insulation.
[0055] The heat conductive layer 28c is made of nickel and formed
on the heat insulation layer 28b. Alternatively, the heat
conductive layer 28c may be made of another material as long as the
heat conductive layer 28c has a higher heat conductivity than at
least the heat insulation layer 28b. For example, the heat
conductive layer 28c may be made of an iron alloy such as stainless
steel, or metal such as aluminum or copper. Alternatively, the heat
conductive layer 28c may be a graphite sheet.
[0056] The heat conductive layer 28c reduces localized unevenness
in surface temperature of the fixing roller 28 caused by uneven
heating by the heater 56. Rapid heat transmission between adjacent
sub-heaters 56a through 56g where heat is not generated reduces
fixing failures of images.
[0057] Moreover, the heat conductive layer 28c has an effect to
increase the temperature of a slightly wider area than an area
heated by the heater 56, thereby compensating a slight shift from
an image. In other words, sizes of and intervals between the
sub-heaters 56a through and 56g of the heater 56 can be set
relatively in a wide range.
[0058] The release layer 28d is formed on an outer surface of the
heat conductive layer 28c to enhance the durability and maintain
the releasing performance. The release layer 28d is made of
fluorine resin such as perfluoroalkoxy (PFA) or
polytetrafluoroethylene (PTFE), and has a thickness of about 20
.mu.m to about 80 .mu.m.
[0059] The pressing roller 30 is constructed of a metal core 30a
and an elastic layer 30b. The metal core 30a is made of iron and
has an outer diameter of about 50 mm and a thickness of about 4 mm.
The elastic layer 30b coats an outer surface of the metal core 30a.
The elastic layer 30b is made of silicone rubber and has a
thickness of about 5 mm. To enhance releasing performance, a
fluorine resin layer having a thickness of about 50 .mu.m may be
formed on a surface of the elastic layer 30b.
[0060] The pressing roller 30 is pressed against the fixing roller
28 by a biasing unit. The heater 56 is pressed against a surface of
the fixing roller 28 by a biasing unit.
[0061] As described later, control of the sub-heaters 56a through
56g according to the image data can enhance energy efficiency.
[0062] If the surface temperature of the fixing roller 28 is hard
to be increased to a predetermined fixing temperature because of
low heating efficiency of the heater 56, a halogen heater 58
disposed in the fixing roller 28 may be used to heat the fixing
roller 28 so that the fixing roller 28 reaches a temperature
slightly lower than the fixing temperature. Then, the heater 56 may
be used to heat and increase the temperature of the fixing roller
28 at a portion corresponding to an imaged area. Accordingly,
overall energy consumption can be reduced.
[0063] If an image is formed across an entire image formation area
on the sheet P, the entire fixing roller 28 is heated, obviating
heating control according to the image data. Hence, the fixing
roller 28 may be heated up to a fixing temperature only by the
halogen heater 58. Alternatively, the halogen heater 58 and the
heater 56 may be simultaneously energized during a warm-up time
only, to further shorten the warm-up time.
[0064] Referring now to FIGS. 4A, 4B, 5A, and 5B, a description is
now given of the heating control, in which the external heating
control unit 42 controls the heater 56 according to the image data
to form an image on the sheet P.
[0065] FIGS. 4A and 4B are plan views of sheets P, illustrating
imaged areas and blank areas of the sheets P.
[0066] FIG. 4A illustrates an image formation pattern including an
imaged area AP, a blank area BP, and an imaged area AP' in this
order from a leading end of the sheet P in a direction indicated by
arrow A (hereinafter referred to as direction A) in which the sheet
P is conveyed. The imaged areas AP and AP' include toner to be
fixed while the blank area BP does not include toner to be
fixed.
[0067] FIG. 4B illustrates another image formation pattern
including an imaged area AP and a blank area BP in this order from
a leading end of the sheet P in the direction A. The imaged area AP
includes toner to be fixed while the blank area BP does not include
toner to be fixed.
[0068] FIGS. 5A and 5B are plan views of sheets P illustrating
imaged areas and blank areas of the sheets P.
[0069] FIG. 5A illustrates an image formation pattern including an
imaged area CP, and a blank area DP in a direction perpendicular to
the direction A, that is, in a longitudinal direction of the fixing
roller 28. The imaged area CP includes toner to be fixed while the
blank area DP does not include toner to be fixed.
[0070] FIG. 5B illustrates another image formation pattern
including imaged areas EP and FP in the direction perpendicular to
the direction A, and an imaged area GP and a blank area HP in this
order from a leading end of the sheet P in the direction A. The
imaged areas EP, FP, and GP include toner to be fixed while the
blank area HP does not include toner to be fixed.
[0071] Referring back to FIG. 4A, when image data of the image
formation pattern is inputted to the external heating control unit
42 from an image processing device, the external heating control
unit 42 controls the power source 40 and the heater 56 such that a
portion of the fixing roller 28 corresponding to the blank area BP
has a lower temperature than portions of the fixing roller 28
corresponding to the imaged areas AP and AP'.
[0072] It is to be noted that a portion of the fixing roller 28
corresponding to an imaged area or a blank area is a portion of the
fixing roller 28 that adheres to the imaged area or the blank area.
In other words, electric power is supplied to all the sub-heaters
56a through 56g so that the portion of the fixing roller 28
corresponding to the imaged area AP, which is distributed over an
entire width of the sheet P, obtains a predetermined fixing
temperature. Then, the electric power is reduced to heat the
portion of the fixing roller 28 corresponding to the blank area BP.
Thereafter, the electric power is supplied again to the sub-heaters
56a through 56g so that the portion of the fixing roller 28
corresponding to the imaged area AP', which is located at a rear
end of the sheet P, reaches the fixing temperature.
[0073] Referring to FIG. 4B, as in FIG. 4A, the electric power is
supplied to all the sub-heaters 56a through 56g so that the portion
of the fixing roller 28 corresponding to the imaged area AP obtains
the predetermined fixing temperature. Then, the electric power is
reduced to heat the portion of the fixing roller 28 corresponding
to the blank area BP.
[0074] Referring to FIG. 5A, the electric power is supplied to the
sub-heaters 56a through 56g such that a portion of the fixing
roller 28 corresponding to the imaged area CP, which is distributed
over half a width of the sheet P, obtains the predetermined fixing
temperature. Specifically, the external heating control unit 42
controls the power source 40 to supply a lower electric power to,
e.g., the sub-heaters 56e through 56g than to the sub-heaters 56a
through 56d such that a portion of the fixing roller 28
corresponding to the blank area DP has a lower temperature than the
portion of the fixing roller 28 corresponding to the imaged area
CP.
[0075] Referring to FIG. 5B, the electric power is supplied to all
the sub-heaters 56a through 56g such that a portion of the fixing
roller 28 corresponding to the imaged area GP, which is distributed
over an entire width of the sheet P, obtains the predetermined
fixing temperature. Thereafter, a larger electric power is supplied
to, e.g., the sub-heaters 56a through 56d than to the sub-heaters
56e through 56g such that a portion of the fixing roller 28
corresponding to the imaged area EP, which is distributed over half
the width of the sheet P, obtains the predetermined fixing
temperature.
[0076] It is to be noted that the electric power is supplied to the
heater 56 to heat a portion of the fixing roller 28 corresponding
to a preliminary heating area M, which is illustrated with hatching
in each of FIGS. 4A, 4B, 5A, and 5B. The preliminary heating area M
allows the sub-heaters 56a through 56d to preliminarily heat their
respective heating areas. The electric power is supplied to the
heater 56 before an imaged area (e.g., imaged area AP) enters the
fixing nip SN. The preliminary heating area M is provided taking
into account the length of the heater 56 in a circumferential
direction thereof and the time taken to warm up the heater 56. The
preliminary heating area M is preferably provided as small as
possible for the energy efficiency.
[0077] Heating control may be performed to completely stop power
supply to the heater 56 so that the heater 56 does not heat the
portions of the fixing roller 28 corresponding to the blank areas
BP, DP, and HP. In such a case, however, the temperature of the
fixing roller 28 might excessively decrease to affect a subsequent
rise to a fixing temperature to heat a subsequent imaged area
(e.g., imaged area AP' of FIG. 4A). Hence, the heater 56 is
stuttered or supplied with a low electric power to maintain the
fixing roller 28 at a predetermined temperature or higher.
[0078] Thus, a lower electric power is supplied to the heater 56 to
heat the portions of the fixing roller 28 corresponding to the
blank areas BP, DP, and HP, thereby enhancing the energy
efficiency.
[0079] According to the first embodiment, the heater 56 contacts
and heats the surface of the fixing roller 28. Alternatively, the
external heating control unit 42 may include an excitation coil and
inverter to inductively heat the fixing roller 28 without
contacting the fixing roller 28. In such a case, the excitation
coil may be prepared by, e.g., winding a Litz wire from 5 times to
15 times. The Litz wire includes about 50 to about 500 conductive
wire strands, individually insulated and twisted together. Each
conductive wire has a diameter of about 0.05 mm to about 0.2 mm.
Such an induction heating method can control the temperature of the
fixing roller 28 according to the image data. Accordingly, a fixing
device 12 employing the induction heating method can enhance the
energy efficiency as in the fixing device 12 according to the first
embodiment.
[0080] Referring now to FIGS. 6 and 7, a description is given of a
fixing device 12 according to a second embodiment.
[0081] FIG. 6 is a schematic sectional view of the fixing device 12
according to the second embodiment.
[0082] In the fixing device 12 according to the second embodiment,
a heater 56 is disposed inside a loop formed by a fixing belt (or
film) 38 to increase the temperature of the fixing belt 38, thereby
heating and fixing an unfixed image formed on a sheet P conveyed at
a fixing nip SN.
[0083] The heater 56 is disposed upstream from the fixing nip SN in
a direction indicated by arrow C (hereinafter referred to as
direction C) in which the fixing belt 38 rotates, because it takes
time for the heat from the heater 56 disposed inside the loop
formed by the fixing belt 38 to reach an outer surface of the
fixing belt 38. Alternatively, the heater 56 may be disposed near
the fixing nip SN. A fixing device employing an external heating
method, such as the fixing device 12 according to the first
embodiment, may also have the heater 56 near the fixing nip SN.
[0084] As illustrated in FIG. 7, the heater 56 serving as a planar
heating unit has multiple sub-heaters, which, in the present
embodiment, are ten sub-heaters 56a' through 56j' arrayed in a
direction perpendicular to a direction in which the sheet P is
conveyed. The sub-heaters 56a' through 56j' are separately
controlled to heat their respective heating areas.
[0085] Referring back to FIG. 6, the fixing belt 38 serving as a
fixing member is constructed of a base 38a, an elastic layer 38b,
and a release layer 38c. The base 38a is made of stainless steel
and has an outer diameter of about 50 mm and a thickness of about
40 .mu.m. Alternatively, the base 38a may be polyimide to enhance
durability and maintain releasing performance. The elastic layer
38b coats an outer surface of the base 38a. The elastic layer 38b
is made of silicone rubber and has a thickness of about 100 .mu.m.
The release layer 38c is formed on the elastic layer 38b to enhance
durability and maintain releasing performance. The release layer
38c is made of fluorine resin such as PFA or PTFE, and has a
thickness of about 20 .mu.m to 80 .mu.m.
[0086] A support member 61 and a nip forming member 60 serving as a
pressure member and facing the fixing nip SN are also disposed
inside the loop formed by the fixing belt 38 to support the fixing
belt 38 in connection with an external member.
[0087] The fixing belt 38 and the components disposed inside the
loop formed by the fixing belt 38, that is, a thermistor 36, the
heater 56, the pressure member 60, and the support member 61, may
constitute a belt unit 38U separably coupled with the pressing
roller 30.
[0088] Referring now to FIG. 8, a description is given of a fixing
device 12 according to a third embodiment.
[0089] FIG. 8 is a schematic sectional view of the fixing device 12
according to the third embodiment.
[0090] As illustrated in FIG. 8, a heater 56 serving as a planar
heating unit is disposed facing a fixing nip SN, thereby also
serving as a pressure member. A configuration of the fixing device
12 according to the third embodiment is otherwise the same as the
fixing device 12 of FIG. 6 according to the second embodiment.
[0091] It is to be noted that the fixing belt 38 illustrated in
FIG. 6 may be configured to be heated by the external heating
method as illustrated in FIG. 2.
[0092] The fixing belt 38 and the components disposed inside a loop
formed by the fixing belt 38, that is, a thermistor 36, the heater
56, and a support member 61, may constitute a belt unit 38U
separably coupled with the pressing roller 30.
[0093] Referring now to FIG. 9, a description is given of a fixing
device 12 according to a fourth embodiment.
[0094] FIG. 9 is a schematic sectional view of the fixing device 12
according to the fourth embodiment.
[0095] As illustrated in FIG. 9, the fixing device 12 includes a
fixing belt 38 serving as a fixing rotation body, a pressing roller
30 serving as a facing member (or facing rotation body) to contact
the fixing belt 38 to form a fixing nip SN, and a heater 56 serving
as a heating member to heat a fixing belt 38. The heater 56
contacts the fixing belt 38 in a substantially flat manner. A
separate pressure roller 39, described in detail below, is disposed
facing the heater 56 outside the fixing belt 38, at a location
other than that of the pressing roller 30.
[0096] The fixing belt 38 is a thin, endless belt member having
flexibility. The belt member is not limited to a belt. The belt
member may be, e.g., a film. Specifically, the fixing belt 38 is
constructed of a base 38a, an elastic layer 38b, and a release
layer 38c. The base 38a is made of stainless steel and has an outer
diameter of about 40 mm and a thickness of about 40 .mu.m.
Alternatively, the base 38a may be made of a resin material such as
polyimide. The elastic layer 38b is made of silicone rubber and has
a thickness of about 100 .mu.m. The release layer 38c is made of
fluorine resin such as PFA or PTFE, and has a thickness of about 5
.mu.m to 50 .mu.m. The elastic layer 38b coats an outer
circumferential surface of the base 38a. The release layer 38c
coats an outer circumferential surface of the elastic layer
38b.
[0097] The pressing roller 30 is constructed of a metal core 30a
and an elastic layer 30b. The metal core 30a is made of iron and
has an outer diameter of about 40 mm and a thickness of about 2 mm.
The elastic layer 30b coats an outer circumferential surface of the
metal core 30a. The elastic layer 30b is made of silicone rubber
and has a thickness of about 5 mm. To enhance releasing
performance, a release layer made of fluorine resin having a
thickness of about 40 .mu.m may be formed on an outer
circumferential surface of the elastic layer 30b.
[0098] A nip forming member 60 serving as a pressure member is
disposed facing the pressing roller 30 inside a loop formed by the
fixing belt 38. Both ends of the nip forming member 60 are
supported by side plates of the fixing device 12. The pressing
roller 30 is pressed against the nip forming member 60 by a
pressing unit such as a pressure lever, thereby forming the fixing
nip SN having a predetermined width in which the fixing belt 38 and
the pressing roller 30 is in pressure contact with each other.
Alternatively, the fixing belt 38 serving as a fixing rotation body
and the pressing roller 30 serving as a facing member may be in
contact with each other without pressure.
[0099] The pressing roller 30 is configured to be driven by a
driving source such as a motor to rotate in a direction indicated
by arrow B (hereinafter referred to as direction B) in FIG. 9. The
driving force generated by the rotation of the pressing roller 30
is transmitted to the fixing belt 38 through the fixing nip SN,
thereby rotating the fixing belt 38 in a direction C in FIG. 9. A
belt support member 61 is disposed inside the loop formed by the
fixing belt 38 to support the fixing belt 38.
[0100] The heater 56 is a sheet or planar heat generator such as a
thermal heater or a ceramic heater. A stay 35 serving as a support
member is disposed inside the loop formed by the fixing belt 38.
The stay 35 supports the heater 56 such that the heater 56 faces an
inner circumferential surface of the fixing belt 38, on an upstream
side from the fixing nip SN in a direction A in which a sheet P is
conveyed. A power source 40 is connected to the heater 56 to supply
electric power to the heater 56. An external heating control unit
42 controls an output from the power source 40. The external
heating control unit 42 is constituted as a microprocessor
including, e.g., a CPU, a ROM, a RAM, and an I/O interface.
[0101] The fixing device 12 includes a first thermistor 36 and a
second thermistor 34. The first thermistor 36 serves as a heater
temperature sensor to detect a temperature of the heater 56. The
second thermistor 34 serves as a belt temperature sensor to detect
a temperature of the fixing belt 38. The first thermistor 36 is
disposed so as to directly contact the heater 56. The second
thermistor 34 is disposed so as to face an outer circumferential
surface of the fixing belt 38, upstream from the heater 56 in the
direction C in which the fixing belt 38 rotates. Temperature data
obtained by the first thermistor 36 and the second thermistor 34 is
inputted to the external heating control unit 42. The external
heating control unit 42 is configured to control an output from the
power source 40 according to the temperature data thus
inputted.
[0102] An image processing unit 90 illustrated in FIG. 9 receives
an image signal transmitted by an image reader or an external
device of the image forming apparatus 2 to perform a predetermined
imaging process. Then, the external heating control unit 42
receives image data from the image processing unit 90. The external
heating control unit 42 controls an output of the heater 56 via the
power source 40 according to the image data.
[0103] A pressure roller 39 is disposed facing the heater 56
outside the fixing belt 38. The pressure roller 39 serves as a
pressure member to apply pressure to the fixing belt 38. The
pressure roller 39 applies pressure to the outer circumferential
surface of the fixing belt 38 toward the heater 56 disposed inside
the loop formed by the fixing belt 38 so that the fixing belt 38
contacts the heater 56. The pressure roller 39 has an outer
diameter of about 15 mm to about 30 mm. The pressure roller 39 is
constructed of a metal core 39a and an elastic layer 39b. The metal
core 39a is made of iron and has an outer diameter of about 8 mm.
The elastic layer 39b coats an outer circumferential surface of the
metal core 39a. The elastic layer 39b is made of silicone rubber
and has a thickness of about 3.5 mm to about 11 mm. To enhance
releasing performance, a release layer made of fluorine resin
having a thickness of about 40 .mu.m may be formed on an outer
circumferential surface of the elastic layer 39b. The pressure
roller 39 is herein pressed against the fixing belt 38 by a
pressing unit. Alternatively, the pressing unit may be omitted so
that the pressure roller 39 contacts the fixing belt 38 without
pressure.
[0104] The fixing belt 38 and the components disposed inside the
loop formed by the fixing belt 38, that is, the stay 35, the
thermistor 36, the heater 56, the nip forming member 60, and the
support member 61, may constitute a belt unit 38U separably coupled
with the pressing roller 30.
[0105] Referring to FIG. 9, a description is now given of basic
operation of the fixing device 12.
[0106] When the image forming apparatus 2 is activated, the power
source 40 starts to supply electric power to the heater 56 while
the pressing roller 30 starts to rotate in the direction B. The
rotation of the pressing roller 30 drives the fixing belt 38 to
rotate in the direction C due to frictional force therebetween.
[0107] Thereafter, when the sheet P carrying an unfixed toner image
G is conveyed to the fixing nip SN formed between the fixing belt
38 and the pressing roller 30 after the foregoing imaging process,
the toner image G formed on the sheet P is fixed onto the sheet P
under heat and pressure in the fixing nip SN. The sheet P is then
outputted from the fixing nip SN, and consequently from the image
forming apparatus 2.
[0108] As described above, the energy efficiency can be enhanced by
controlling the temperature of a fixing member (e.g., fixing roller
28), particularly by decreasing the temperature of portions of the
fixing member corresponding to the preliminary heating area M and a
blank area according to data obtained by associated imaging
equipment. In addition, such control can prevent typical problems
arising from the foregoing types of fixing devices, such as a
decrease in durability of the fixing member and a pressing member
(e.g., pressing roller 30) and an adverse thermal effect on
surrounding components caused by an excessive temperature increase
at a portion of the fixing member corresponding to a blank
area.
[0109] According to the foregoing embodiments, the energy
efficiency is enhanced by reducing a power supply to the heater 56
to heat a portion of the fixing member corresponding to a blank
area. As described above, a preliminary heating area M is provided
in a blank area (e.g., blank area BP of FIG. 1) followed by an
imaged area (e.g., imaged area AP' of FIG. 1) to allow sub-heaters
(e.g., 56a through 56g) to preliminarily heat their respective
heating areas before the imaged area enters a fixing nip SN.
Accordingly, the energy efficiency is preferably enhanced by
downsizing the preliminary heating area M.
[0110] Referring now to FIGS. 10 through 12, a detailed description
is given of the preliminary heating area M.
[0111] FIG. 10 is a schematic sectional view of a fixing device 12
employing an external heating method.
[0112] The fixing device 12 includes, e.g., a fixing roller 28
serving as a fixing member, a pressing roller 30, and a heater 56
serving as an external heating unit. Alternatively, the fixing
device 12 may have a configuration as illustrated in FIG. 6, in
which a fixing belt serving as a fixing member is heated from
within.
[0113] FIG. 11 is a plan view of a sheet P, illustrating an image
formation pattern including a blank area BP, an imaged area AP, a
blank area BP', and an imaged area AP' in this order from a leading
end of the sheet P in a direction A in which the sheet P is
conveyed.
[0114] Preliminary heating areas M1 and M2 are provided in the
blank areas BP and BP', respectively.
[0115] FIG. 12 is a graph of a relationship between target
temperatures and portions of the fixing roller 28.
[0116] A horizontal axis indicates surface portions of the fixing
roller 28. A vertical axis indicates target control temperatures at
the portions of the fixing roller 28. Portions AP and AP'
correspond to the imaged areas AP and AP' of FIG. 11. Portions BP
and BP' correspond to the blank areas BP and BP' of FIG. 11. As
illustrated in FIG. 12, a first target temperature is maintained
for the imaged areas AP and AP'. A second target temperature is
maintained for the blank areas BP and BP'. The second target
temperature is lower than the first target temperature and higher
than a room temperature.
[0117] Portions Q and Q' indicate heated portions of the fixing
roller 28. The portion Q includes the portion A and a portion
corresponding to a preliminary heating area M1. In other words, a
relation of Q=A+M1 is satisfied. The portion Q' includes the
portion A' and a portion corresponding to a preliminary heating
area M2. In other words, a relation of Q'=A'+M2 is satisfied. In
the light of a width H of the heater 56 illustrated in FIG. 10 and
a warm-up time for the heater 56, the preliminary heating areas M1
and M2 are provided to allow the portions AP and AP', respectively,
to have a sufficiently increased surface temperature.
[0118] The following describes some examples of the preliminary
heating area M applied to the fixing devices 12 according to the
foregoing embodiments.
[0119] Referring now to FIG. 13, a description is given of a
preliminary heating area M according to a first example to enhance
the energy efficiency.
[0120] FIG. 13 is a graph of a relationship between target
temperatures and portions of a fixing member (e.g., fixing belt
38), particularly illustrating the relationship between the target
temperatures and the portions of the fixing member corresponding to
preliminary heating areas MM and MS.
[0121] According to the first example, when an image (e.g., image
illustrated in FIG. 11) is fixed on a sheet P, an external heating
control unit 42 changes the size of the preliminary heating area M
according to detected data of a fixing device 12 incorporating the
external heating control unit 42. In FIG. 13, a temperature change
in a portion of the fixing member corresponding to a preliminary
heating area MM is indicated by a solid line. A temperature change
in a portion of the fixing member corresponding to a preliminary
heating area MS is indicated by a broken line. For example, the
preliminary heating area MM is provided in an initial state upon
activation of an image forming apparatus 2. In such a state, the
fixing member has a third target temperature that is close to a
room temperature or lower than a fixing temperature. The
preliminary heating area MM has a sufficient size to increase the
temperature of the fixing member to a first target temperature.
[0122] It is to be noted that the preliminary heating area M is set
to a predetermined size before an imaged area enters a fixing nip
SN. If the preliminary heating area M is set to a size smaller than
the predetermined size, the fixing member might not reach the first
target temperature when the imaged area enters the fixing nip SN,
causing fixing failures.
[0123] Specifically, the external heating control unit 42
appropriately sets the size of the preliminary heating area M
according to the temperature of a contact heater 56 detected by a
thermistor 36. As indicated by the solid line in FIG. 13, the
preliminary heating area MM, herein defined as a reference
preliminary heating area, is provided to allow the fixing member to
sufficiently heat the imaged area when the heater 56 has a low
temperature, particularly, in the initial state of the image
forming apparatus 2. Whereas, when the temperature of the fixing
member increases faster than an initial setting, the preliminary
heating area MS is provided for heating control of the heater 56,
as indicated by the broken line in FIG. 13. The preliminary heating
area MS is smaller than the preliminary heating area MM. For
example, the preliminary heating area MS is provided when the
heater 56 has a higher temperature than a predetermined temperature
due to a continuous printing operation. Accordingly, the energy
efficiency can be enhanced when the heater 56 maintains a
sufficient temperature to heat an imaged area. For example, the
energy efficiency can be enhanced when multiple sheets P
continuously pass through the fixing nip SN.
[0124] To heat the preliminary heating area MM, an electric power
of, e.g., 200 Ws (100 watts.times.2 seconds) is supplied to the
heater 56. Whereas, to heat the preliminary heating area MS, an
electric power of, e.g., 100 Ws (100 watts.times.1 second) is
supplied to the heater 56. Thus, the energy efficiency can be
enhanced by shortening the duration of power supply while image
forming operation is reliably performed. It is to be noted that the
first target temperature is e.g., 120.degree. C., the second target
temperature is e.g., 90.degree. C., and the third target
temperature is e.g., 80.degree. C. or a room temperature.
[0125] In the foregoing descriptions with reference to FIGS. 11
through 13, an image is uniformly formed in an axial direction of a
roller (e.g., fixing roller 28), i.e., in a direction perpendicular
to the direction A in which the sheet P is conveyed. Alternatively,
the image may be divided into multiple imaged areas in the axial
direction. In such a case, different preliminary heating areas M
may be provided to the imaged areas based on detected temperatures
of sub-heaters of the heater 56.
[0126] If the detected temperatures of the sub-heaters of the
heater 56 are lower than a predetermined temperature, the external
heating control unit 42 may set a preliminary heating area M to be
larger than the preliminary heating area MM to obtain a reliable
image fixability.
[0127] FIG. 14 is a flowchart of a process for setting the
preliminary heating area M according to detection results of the
sub-heaters 56a through 56g.
[0128] Sub-heaters 56.sub.i (i=1 to 7) correspond to the
sub-heaters 56a through 56g. At first, the reference preliminary
heating area MM is set for all the sub-heaters 56.sub.1 through
56.sub.7. The thermistor 36 detects a temperature T.sub.i (i=1 to
7) of each sub-heater 56.sub.i in a predetermined timing.
[0129] Thereafter, the external heating control unit 42 obtains
T.sub.i (i=1 to 7) (S1). Then, the external heating control unit 42
firstly determines a temperature T.sub.i of the sub-heater 56.sub.i
where i=1 (S2). If the temperature T.sub.1 is equal to or lower
than a threshold .alpha. (No in S3) and equal to or higher than a
threshold .beta. (No in S4), the external heating control unit 42
maintains the preset preliminary heating area MM (S5). In such a
case, the difference between the temperature T.sub.1 and the
threshold .alpha. is small enough to obviate changes from the
reference preliminary heating area MM. If the temperature T.sub.1
exceeds the threshold .alpha. (Yes in S3), the external heating
control unit 42 sets the preliminary heating area MS that is
smaller than the reference preliminary heating area MM (S6),
because the sub-heater 56.sub.1 has a temperature higher than a
predetermined temperature. If the temperature T.sub.1 is lower than
the threshold .beta. (Yes in S4), the external heating control unit
42 sets a preliminary heating area ML that is larger than the
reference preliminary heating area MM (S7), because the sub-heater
56.sub.1 has a temperature lower than the predetermined
temperature. It is to be noted that a relation of .alpha.>.beta.
is satisfied. Then, the external heating control unit 42 determines
a temperature T.sub.i of the sub-heater 56.sub.i where i=2 (S8, S9,
and back to S3). The foregoing steps S3 to S9 are repeated to set
target temperatures of each sub-heater 56.sub.i (i=1 to 7) to heat
portions of the fixing member corresponding to an imaged area and a
blank area.
[0130] The temperatures of all the sub-heaters 56a through 56g are
herein detected. Alternatively, a temperature of one of the
sub-heaters 56a through 56g may be selectively detected to set the
preliminary heating area M.
[0131] A description is now given of a preliminary heating area M
according to a second example to enhance the energy efficiency. The
external heating control unit 42 sets the size of the preliminary
heating area M according to the voltage of a commercial power
source 40 detected by a sensor. Specifically, the external heating
control unit 42 sets the preliminary heating area M to be smaller
than the preliminary heating area MM when the detected voltage is
high. The voltage is detected, e.g., when an image forming
apparatus 2 is activated. In addition, the voltage may be detected
per second except during an imaging process. Such control is
particularly effective when an alternating-current (AC) voltage is
directly applied to a heater 56 serving as a heating element from
the power source 40. For example, such a smaller preliminary
heating area M is provided when the voltage increases from 100 V to
110 V, i.e., about 120% of electric power is supplied.
[0132] Thus, the energy efficiency can be enhanced, e.g., when
devices disposed around the image forming apparatus 2 are
deactivated and the power source 40 is in a good condition.
[0133] Whereas, if the voltage of the power source 40 is low, a
larger preliminary heating area M is provided to obtain a reliable
image fixability.
[0134] According to the first example, a smaller preliminary
heating area (i.e., preliminary heating area MS) is provided when
the thermistor 36 detects a higher temperature than a predetermined
temperature. According to the second example, the external heating
control unit 42 has multiple threshold temperatures to change the
size of the preliminary heating area M, and correlatively changes
the size of the preliminary heating area M according to the
temperature detected by the thermistor 36. Accordingly, the fixing
device 12 can perform reliable heating operation under wider
operational conditions, thereby enhancing the energy efficiency and
obtaining high image quality.
[0135] This disclosure has been described above with reference to
specific exemplary embodiments. It is to be noted that this
disclosure is not limited to the details of the embodiments
described above, but various modifications and enhancements are
possible without departing from the spirit and scope of the
invention. It is therefore to be understood that this disclosure
may be practiced otherwise than as specifically described herein.
For example, elements and/or features of different illustrative
exemplary embodiments may be combined with each other and/or
substituted for each other within the scope of this invention. The
number of constituent elements and their locations, shapes, and so
forth are not limited to any of the structure for performing the
methodology illustrated in the drawings.
* * * * *